The present invention relates to a position sensorless motor control apparatus which drives a motor for rotation by estimating rotor angle without using position sensors. More particularly, the invention relates to a position sensorless motor control apparatus that achieves high resolution and high accuracy angle estimation, achieves angle estimation even in the presence of phase voltage saturation, and achieves high accuracy angle estimation even-when a back electromotive force constant changes.
Brushless motors which do not use mechanical commutation mechanisms need to be electrically commutated based on rotor angle.
In conventional motor control apparatuses, position sensors such as Hall elements, resolvers, or optical encoders mounted on brushless motors have been used to obtain rotor angle information. The provision of such a position sensor has necessarily added to the cost and increased the size of the brushless motor.
Position sensorless motor control apparatuses that achieve reduced cost and reduced size by eliminating the position sensor are known in the art, including one disclosed in Japanese Unexamined Patent Publication No. 64-43095 (hereinafter referred to as the prior art 1) and one described in xe2x80x9cCollection of Papers, The Institute of Electrical Engineers,xe2x80x9d Vol. 117-D, No. 1, pp. 98-104, 1997 (hereinafter referred to as the prior art 2). These prior art position sensorless motor control apparatuses will be described below. In the following description, some of the value names used in the above cited literature are changed to maintain consistency with those used in the embodiments of the present invention.
These prior art position sensorless motor control apparatuses are designed to control Y-connected three-phase brushless motors.
A block diagram of the, position sensorless motor control apparatus of the prior art 1 is shown in FIG. 27, and a timing chart for the same is shown in FIG. 28. In FIG. 28, some of the signal names are changed for the convenience of comparison with the present invention.
In FIG. 27, the position sensorless motor control apparatus of this prior art first detects phase currents (iu, iv, and iw) flowing through stator windings for the respective phases, phase voltages (vu, vv, and vw) applied to the respective phase stator windings, and a voltage (vn) at a neutral point. Next, the following equations (1), (2), and (3) are calculated to obtain back electromotive force values eu, ev, and ew of the voltages induced in the respective phase stator windings. In the equations, R designates the resistance and L the inductance. Further, d(iu)/dt, d(iv)/dt, and d(iw)/dt are the time derivatives of iu, iv, and iw, respectively.
eu=vuxe2x88x92vnxe2x88x92Rxc2x7iuxe2x88x92Lxc2x7d(iu)/dtxe2x80x83xe2x80x83(1)
ev=vvxe2x88x92vnxe2x88x92Rxc2x7ivxe2x88x92Lxc2x7d(iv)/dtxe2x80x83xe2x80x83(2)
ew=vwxe2x88x92vnxe2x88x92Rxc2x7iwxe2x88x92Lxc2x7d(iw)/dtxe2x80x83xe2x80x83(3)
The back electromotive force values eu, ev, and ew are input to a comparator circuit 35 (FIG. 27). The comparator circuit 35 compares the back electromotive force values eu, ev, and ew with the respective back electromotive force values multiplied by a predetermined constant k (0xe2x89xa6k), i.e., kxc2x7eu, kxc2x7ev, and kxc2x7ew, to determine their magnitude relationships, and outputs signals (b) C1, (c) C2, (d) C3, (e) C4, (f) C5, and (g) C6 representing the results of the comparisons (FIG. 28). These signals are input to a logic circuit 36 (FIG. 27). The logic circuit 36 outputs drive signals (h) DSU+, (i) DSUxe2x88x92, (j) DSV+, (k) DSVxe2x88x92, (l) DSW+, and (m) DSWxe2x88x92 for driving an output unit 16 (FIGS. 27) for the stator windings (FIGS. 27 and 28). The currents flowing through the stator windings are controlled by the drive signals, and the rotor rotates in a prescribed direction.
The prior art 1 compares the magnitudes of the respective back electromotive forces and determines the energization period of each phase, but does not have an angle estimation unit for estimating the rotor angle of the motor. In the timing chart for (b) C1 in FIG. 28, a high period of C1 is shown, but no detailed information within the high period of C1 is presented that is, whether C1 is currently at the beginning, in the middle, or at the end, of the high period is not known. Furthermore, since the angular velocity of the motor is not detected, it is not known how long the high period of C1 will last. It is only possible to know which of the signals C1 to C6 is high at a particular point in time.
Accordingly, the motor cannot be driven with a sinusoidal or like waveform for smooth rotation. In embodiment 1, the voltage applied to each phase of the motor during its energization period is constant.
One object of the present invention is to drive a motor smoothly by estimating the angle of the motor and driving the motor with a sinusoidal waveform.
A block diagram of the position sensorless motor control apparatus of the prior art 2 is shown in FIG. 29, and an analytical model of the motor and its driving circuitry is shown in FIG. 30.
In FIG. 29, the prior art 2 first obtains an error signal, xcex94xcfx89=(dxcex8/dt)xe2x88x92(dxcex8mb/dt), representing the difference between a target angular velocity (dxcex8/dt) and the estimated angular velocity (dxcex8mb/dt) output from an estimated model, and supplies the error signal xcex94xcfx89 to a velocity control block (PI control circuit). The velocity control block outputs a target current for generating the torque required to achieve the target angular velocity. Actual current i is subtracted from the target current The resulting difference xcex94i is input to a current control block (PI control). The current control block outputs the voltage required to flow the target current as a voltage expressed on xcex3xe2x88x92xcex4 axes. This required voltage is summed with the back electromotive force (em) output from the estimated model. The sum voltage expressed on the xcex3xe2x88x92xcex4 axes is first converted into voltages on u, v, and w axes representing the voltages to be applied to the respective stator windings, and then, these voltages on the u, v, and w axes are actually applied to the respective stator windings of the motor.
As described above, the u, v, and w axes are stationary axes corresponding to the respective phases of the stator windings.
The xcex3 and xcex4 axes are coordinate axes with the origin at the center of the magnetic dipole of the rotor of the brushless motor model estimated by the position sensorless motor control apparatus, the direction of the xcex3 axis being the same as the direction of the estimated rotor""s magnetic dipole (i.e., the axis joining the S pole to the N pole) and the xcex4 axis being advanced relative to the xcex3 axis by 90 degrees in the positive direction (in the counterclockwise direction), and the coordinate axes rotates with the estimated rotor.
Likewise, the d and q axes are coordinate axes with the origin at the center of the magnetic dipole of the actual rotor of the motor, the direction of the d axis being the same as the direction of the actual rotor""s magnetic dipole (i.e., the axis joining the S pole to the N pole) and the q axis being advanced relative to the d axis by 90 degrees in the positive direction (in the counterclockwise direction), and the coordinate axes rotates with the actual rotor.
In the feedback loop shown in FIG. 29, the phase currents flowing in the stator windings of the respective phases are detected, and the phase current values are coordinate converted to generate a xcex3-axis current value ixcex3 and a xcex4-axis current value ixcex4.
The relationships between the currents ixcex3, ixcex4 and the voltages vxcex3, vxcex4 can be expressed by the following equations (79) and (80) (where ixcex3 and ixcex4 are the xcex3-axis current component and the xcex4-axis current component, respectively). xcex8m is the estimated rotor angle.
vxcex3={R+Lxcex3(dxcex8m/dt)+Lxcex3(d/dt)}ixcex3+{xe2x88x92Lxcex4(dxcex8m/dt)xe2x88x92Lxcex3xcex4(d/dt)}ixcex4+e(xe2x88x92sin xcex94xcex8)xe2x80x83xe2x80x83(79)
vxcex4={Lxcex3(dxcex8m/dt)xe2x88x92Lxcex3xcex4(d/dt)}ixcex3+{Rxe2x88x92Lxcex3xcex4(dxcex8m/dt)+Lxcex4(d/dt)}ixcex4+e(cos xcex94xcex8)xe2x80x83xe2x80x83(80)
Setting Lxcex3xcex4≈0, Lxcex3≈Ld, Lxcex4≈Lq, and xcex94xcex8=xcex8xe2x88x92xcex8m (where xcex8 is the actual rotor angle, and am is the estimated rotor angle), then ixcex3 and ixcex4 (the actual stator winding currents expressed on the xcex3xe2x88x92xcex4 axes) are given as
ixcex3(n)=(1xe2x88x92Rxc2x7T/Ld)xc2x7ixcex3(nxe2x88x92i) +(dxcex8m/dt)xc2x7Lqxc2x7T/Ldxc2x7ixcex4(nxe2x88x921) +(T/Ld)xc2x7vxcex3(nxe2x88x921) +(Txc2x7e/Ld)xc2x7(sin xcex94xcex8)xe2x80x83xe2x80x83(81)
ixcex4(n)={xe2x88x92(dxcex8m/dt)xc2x7(Ldxc2x7T/Lq)xc2x7ixcex3(nxe2x88x921) +(1xe2x88x92Rxc2x7T/Lq)xc2x7ixcex4(nxe2x88x921) +(T/Lq)xc2x7vxcex4(nxe2x88x921) +(Txc2x7e/Lq)xc2x7(xe2x88x92cos xcex94xcex8)xe2x80x83xe2x80x83(82)
where T is the calculation interval, that is, the time difference between ixcex3(n) and ixcex3(nxe2x88x921).
Likewise, by applying motor constants to the xcex3-axis and xcex4-axis voltage equations expressing the brushless motor model, the xcex3-axis current model value ixcex3m (estimated xcex3-axis current component) and the xcex4-axis current model value ixcex4m (estimated xcex4-axis current component) are expressed as shown by equations (83) and (84).
ixcex3m(n)=(1xe2x88x92Rxc2x7T/Ld)xc2x7ixcex3(nxe2x88x921) +{(dxcex8m/dt)xc2x7Lqxc2x7T/Ldxc2x7ixcex4(nxe2x88x921) +(T/Ld)xc2x7vxcex3(nxe2x88x921) +(Txc2x7em/Ld)xc2x70xe2x80x83xe2x80x83(83)
ixcex4m(n)={xe2x88x92(dxcex8m/dt)xc2x7(Ld T/Lq)xc2x7ixcex3(nxe2x88x921) +(1xe2x88x92Rxc2x7T/Lq)xc2x7ixcex4(nxe2x88x921) +(T/Lq)xc2x7vxcex4(nxe2x88x921) +(Txc2x7em/Lq)xc2x71xe2x80x83xe2x80x83(84)
(These equations are the same as the equations of ixcex3(n) and ixcex4(n) when xcex94xcex8=0.)
From equations (81) to (84), the xcex3-axis current error value, xcex94ixcex3(n)=ixcex3(n)xe2x88x92ixcex3m(n), and the xcex4-axis current error value, xcex94ixcex4(n)=ixcex4(n)xe2x88x92ixcex4m(n), representing the errors of the estimated xcex3-axis current model value ixcex3m and xcex4-axis current model value ixcex4m relative to the actual xcex3-axis current value ixcex3 and xcex4-axis current value ixcex4, respectively, are given as                                                                         Δ                ⁢                                  xe2x80x83                                ⁢                i                ⁢                                  xe2x80x83                                ⁢                                  γ                  ⁡                                      (                    n                    )                                                              =                              xe2x80x83                            ⁢                                                (                                      T                    /                    Ld                                    )                                ·                                  e                  ⁡                                      (                                          sin                      ⁢                                              xe2x80x83                                            ⁢                      Δ                      ⁢                                              xe2x80x83                                            ⁢                      θ                                        )                                                                                                                          ≈                              xe2x80x83                            ⁢                                                (                                      T                    /                    Ld                                    )                                ·                                  e                  (                                      xe2x80x83                                    ⁢                                      Δ                    ⁢                                          xe2x80x83                                        ⁢                    θ                                    )                                                                                        (        85        )                                                                                    Δ                ⁢                                  xe2x80x83                                ⁢                i                ⁢                                  xe2x80x83                                ⁢                                  δ                  ⁡                                      (                    n                    )                                                              =                              xe2x80x83                            ⁢                                                (                                      T                    /                    Lq                                    )                                ·                                  (                                      em                    -                                                                  e                        ·                        cos                                            ⁢                                              xe2x80x83                                            ⁢                      Δ                      ⁢                                              xe2x80x83                                            ⁢                      θ                                                        )                                                                                                        ≈                              xe2x80x83                            ⁢                                                                    (                                          T                      /                      Lq                                        )                                    ·                  Δ                                ⁢                                  xe2x80x83                                ⁢                e                                                                        (        86        )            
As shown in the above equations, the velocity electromotive force estimation error xcex94e is proportional to xcex94ixcex4(n) and the position estimation error xcex94xcex8 is proportional to xcex94ixcex3(n).
After all, the prior art 2 estimates the back electromotive force (electromotive force) based on equation (86) and the rotor angle based on equation (85), as will be described later.
In the actual motor, since the back electromotive force varies as a function of temperature, the back electromotive force e and the voltages vxcex3 and vxcex4 vary with temperature. On the other hand, in the estimated model which does not take temperature variations into account, neither the back electromotive force em nor the voltages vxcex3m, vxcex4m vary with temperature.
Though, actually, the back electromotive force em vary with temperature and, consequently, vxcex3(nxe2x88x921) and vxcex4(nxe2x88x921) vary with temperature, the equations (83) and (84), expressing the estimated values that do not vary with temperature, are respectively subtracted from the equations (81) and (82), expressing the actually measured values that vary with temperature, to derive the equations (85) and (86); therefore, xcex94ixcex3(n) and xcex94ixcex4(n) are expressed as varying proportionally to e and xcex94e despite the fact that they change differently with temperature. As a result, the variation of the back electromotive force with temperature causes errors in the estimated angle.
In the prior art 2, the estimated back electromotive force em(n) and estimated angle xcex8m (n) are obtained by multiplying the current errors xcex94ixcex3(n) and xcex94ixcex4(n) of equations (85) and (86) by the velocity electromotive force constant Kv and position estimation gain Kp.
em(n)=em(nxe2x88x921)xe2x88x92Kpxcex94ixcex4(n)xe2x80x83xe2x80x83(87)
xcex8m(n)=xcex8m(nxe2x88x921)+(T/Kv)xc2x7em(n) +Kpxc2x7sgn{xcex8m(nxe2x88x921)}xc2x7xcex94ixcex3(n)xe2x80x83xe2x80x83(88)
sgn{xcex8m(nxe2x88x921)}=1: xcex8m(nxe2x88x921)xe2x89xa70 xe2x88x921: xcex8m(nxe2x88x921) less than 0 
In FIG. 29, the actually measured ixcex3 and ixcex4 are fed back to the estimated model (velocity electromotive force, position, and velocity estimation) for calculation of the error signals relative to the estimated ixcex3m and ixcex4m that the estimated model has, and the resultant xcex94ixcex3(n) and xcex94ixcex4(n) are substituted into the equations (87) and (88) to obtain the velocity electromotive force (back electromotive force) em(n) and the estimated angle xcex8m(n), respectively.
From the equations (87) and (88), the estimated angular velocity (dxcex8m/dt) is obtained by the following equation.                                                                                           ⅆ                  θ                                ⁢                                  xe2x80x83                                ⁢                                  m                  /                                      ⅆ                    t                                                              =                              xe2x80x83                            ⁢                                                (                                      1                    /                    T                                    )                                ⁢                                  {                                                            θ                      ⁢                                              xe2x80x83                                            ⁢                                              m                        ⁡                                                  (                          n                          )                                                                                      -                                          θ                      ⁢                                              xe2x80x83                                            ⁢                                              m                        ⁡                                                  (                                                      n                            -                            1                                                    )                                                                                                      }                                                                                                                        xe2x80x83                            ⁢                              =                                                      {                                                                  em                        ⁡                                                  (                          n                          )                                                                    /                      Kv                                        }                                    +                                                                                                                        xe2x80x83                            ⁢                                                                    (                                          Kp                      /                      T                                        )                                    ·                  sgn                                ⁢                                                      {                                          θ                      ⁢                                              xe2x80x83                                            ⁢                                              m                        ⁡                                                  (                                                      n                            -                            1                                                    )                                                                                      }                                    ·                  Δ                                ⁢                                  xe2x80x83                                ⁢                i                ⁢                                  xe2x80x83                                ⁢                γ                ⁢                                  xe2x80x83                                ⁢                                  (                  n                  )                                                                                        (        89        )            
In the prior art 2, the estimated angular velocity (dxcex8m/dt) is passed through an LPF (low pass filter) to eliminate the effects of noise before being output.
As described above, the prior art 2 obtains the velocity electromotive force (back electromotive force) em(n) and estimated angle xcex8m(n) from the equations (87) and (88), and the estimated angular velocity (dxcex8m/dt) from the equation (89).
In practice, however, the velocity electromotive force constant Kv used as a constant coefficient in the equations (87) and (88) has temperature dependence. The drawback is therefore that the angle estimation error of the estimated model increases due to such factors as changes in environmental temperature between summer and winter and the increase of temperature inside the apparatus from the start of the motor operation to the time steady state operation is reached.
Further, as described in the literature of the prior art 2, the rotor angle of the motor is estimated using voltages expressed on the xcex3xe2x88x92xcex4 axes. This therefore requires that the voltages expressed on the xcex3xe2x88x92xcex4 axes be converted to the stator winding phase voltages expressed on the u, v, and w axes, and conversely, the stator winding phase voltages expressed on the u, v, and w axes be converted to signals on the xcex3xe2x88x92xcex4 axes.
The position sensorless motor control apparatus of the prior art 1 can detect the angle in the presence of phase voltage saturation. However, since it only determines the phase to be energized based on the logic of the comparison results created based on the obtained back electromotive force values eu, ev, and ew, the rotor angle information only provides information concerning the point at which the phase voltage is switched. Accordingly, in the case of the 150-degree energization method described in an embodiment of the prior art 1, if all pieces of information were combined it was only possible to achieve a resolution of 30 degrees in terms of electrical angle (information concerning to which phase the current is to be supplied).
Furthermore, in the prior art 1, angle estimation is not performed, but the angle is only detected and square wave voltages are applied to the stator windings of the motor. This caused torque ripple because square wave currents were supplied to the stator windings.
If sinusoidal currents are to be supplied to the stator windings, angle estimation must be performed.
Moreover, since the velocity information was created based on the low resolution angle, velocity controllability was poor.
The position sensorless motor control apparatus of the prior art 2 can estimate the angle with high resolution. However, the prior art 2 estimates the rotor angle of the motor by using voltages expressed on the xcex3xe2x88x92xcex4 axes (rotating coordinate system). This requires that the voltages expressed on the xcex3 and xcex4 axes be converted to coordinates on the u, v, and w axes expressing the voltages applied to the respective phases and, conversely, the signals expressed on the u, v, and w axes be converted to signals expressed on the xcex3 and xcex4 axes.
If the motor is driven with a sinusoidal waveform, it is easy to convert the voltages expressed on the xcex3xe2x88x92xcex4 axes to the stator winding phase voltages expressed on the u, v, and w axes and, conversely, the stator winding phase voltages expressed on the u, v, and w axes to signals expressed on the xcex3xe2x88x92xcex4 axes. However, if the motor is to be driven with a non-sinusoidal waveform (for example, a trapezoidal or square waveform), the problem is that it is extremely difficult to convert the trapezoidal or square waveform, for example, applied to the stator windings of the motor, to a waveform on the xcex3 and xcex4 axes.
Furthermore, in the prior art 2, the equations (81), (82), (83), and (84) are given on the assumption that the signal waveform is sinusoidal. This has lead to the problem that if the method of the prior art 2 is applied to the case of a signal waveform other than a sinusoidal waveform, an angle estimation error occurs.
As a result, if the motor angular velocity or output torque, for example, increases and the required phase voltage becomes large, the phase voltage saturates; this causes, in particular, the voltage waveform of each. phase to lose its sinusoidal shape, rendering accurate angle estimation impossible, and therefore it has not been possible to achieve high angular velocity or large output torque.
Further, the position sensorless motor control apparatus of the prior art 2 estimates the angle based on the equations (87) and (88). Therefore, since the velocity electromotive force constant Kv varies with temperature, as earlier noted there occurs the problem that the angle estimation error increases due to environmental temperature changes or temperature rises inside the apparatus.
Phase resistance value R also varies with temperature, but since the magnitude of the term of the phase resistance in the phase voltage equations is small, it has little effect on the angle estimation.
In this specification, the term xe2x80x9cphase voltage equationxe2x80x9d refers to any equation relating to the stator winding phase of the motor. The phase voltage equation includes, for example, a strict equation such as equation (26), as well as a simplified equation such as equation (50). The term is used with a broader concept to include equations other than those described in this specification as long as they are equations relating to the stator winding phase of the motor.
In this specification and in the description of the appended claims, the term xe2x80x9cequationxe2x80x9d and the term xe2x80x9cfunctionxe2x80x9d are used with the same meaning.
Further, in the prior art 2, the estimated back electromotive force em is added in the path between the point where the target angular velocity (dxcex8/dt) is input and the point where the voltage is applied to each phase of the motor.
However, since the back electromotive force e is a value that varies with temperature, the addition of the estimated back electromotive force em that does not consider temperature changes involves the problem that the residual error of the estimated angle increases when the temperature changes.
The present invention has been devised to solve the above-enumerated problems, and it is an object of the invention to provide a position sensorless motor control apparatus that achieves high resolution and high accuracy angle estimation, achieves high accuracy angle estimation even in the presence of phase voltage saturation, and achieves high accuracy angle estimation even when the back electromotive force constant changes.
A position sensorless motor control apparatus applies to each stator winding of a motor a voltage derived by a function that takes a target current of the stator winding of the motor, an actually measured current of the stator winding, and an estimated rotor angle of the motor as variables.
According to this invention, a position sensorless motor control apparatus can be achieved that estimates the angle with high accuracy over a wide temperature range.
A position sensorless motor control apparatus estimates the angle by using a signal derived from a parameter relating to each stator winding of the motor.
According to this invention, a position sensorless motor control apparatus can be achieved that estimates the angle with high accuracy over a wide voltage range or current range extending into a region where the phase voltage, etc. saturate.
A position sensorless motor control apparatus calculates an angle error between an estimated signal (estimated model) and a signal based on measure data, and corrects the estimated signal in such a manner as to reduce the angle error.
According to this invention, a position sensorless motor control apparatus can be achieved that estimates the angle with high accuracy over a wide voltage range or current range extending into a region where the phase voltage, etc. saturate, by using, for example, an angle estimating unit having an estimated signal of sinusoidal waveform.
In this specification and in the description of the appended claims, the term xe2x80x9cestimated signalxe2x80x9d and the term xe2x80x9cestimated modelxe2x80x9d are used with the same meaning.
A position sensorless motor control apparatus calculates an angle error and an amplitude error between the estimated signal and the signal based on measured data, and corrects the estimated signal in such a manner as to reduce the angle error and amplitude error.
According to this invention, a position sensorless motor control apparatus can be achieved that is capable of estimating the correct angular velocity even when changes occur in the load or in the angular velocity.
A position sensorless motor control apparatus corrects, based on measured data, the value of at least one of coefficients in a function forming the estimated signal (estimated model).
According to this invention, a position sensorless motor control apparatus can be achieved that has high angle estimation accuracy.
A position sensorless motor control apparatus forms an angle estimation control system that contains neither a back electromotive force nor an element substantially equivalent to the back electromotive force.
According to this invention, a position sensorless motor control apparatus can be achieved that estimates the angle with high accuracy over a wide temperature range.
A position sensorless motor control apparatus selects one of the plurality of stator windings of the motor and corrects the estimated signal based on the data of the selected phase.
According to this invention, a position sensorless motor control apparatus can be achieved that estimates the angle with high resolution and high accuracy for any rotor angle.
A position sensorless motor control apparatus determines that the motor is not controlled properly when the magnitude of an error signal exceeds a certain range.
According to this invention, a position sensorless motor control apparatus can be achieved that can quickly recover from a faulty condition by taking appropriate action, such as decelerating the motor, when the angle estimation control system drifts outside a pull-in range or hold range.
A position sensorless motor control apparatus corrects the estimated signal by using a value obtained by multiplying the error signal by a gain having a defined correspondence with the angular velocity.
According to this invention, a position sensorless motor control apparatus can be achieved that estimates the angle with high accuracy over a wide velocity range.
A position sensorless motor control apparatus imposes a limit to the correction amount of the estimated signal.
According to this invention, a position sensorless motor control apparatus can be achieved that is relatively unaffected by variations due to noise.
A position sensorless motor control apparatus causes the phase current values detected by current sensors to be interchanged between at least two stator winding phases and also causes voltage command values to be interchanged between the at least two stator winding phases when a rotational direction command indicates switching from a forward direction to a reverse direction.
According to this invention, a position sensorless motor control apparatus can be achieved that accomplishes switching between the forward and reverse rotations with a small number of elements involved, and that allows most of the circuit block or program block to be used for both forward and reverse rotations.
A position sensorless motor control apparatus takes as the estimated signal a back electromotive force derived by subtracting components other than the back electromotive force from the measured or calculated voltage of the stator winding.
According to this invention, a position sensorless motor control apparatus can be achieved that estimates the angle with high accuracy over a wide temperature range.
The term xe2x80x9ccalculated voltage of the stator windingxe2x80x9d includes the target voltage of the stator winding.
A position sensorless motor control apparatus has an estimated signal whose waveform is the same as the waveform of a stator winding current.
According to this invention, a position sensorless motor control apparatus can be achieved that estimates the angle with high accuracy over a wide temperature range.
The invention has an estimated signal whose waveform is the same as the waveform of a phase voltage.
According to this invention, a position sensorless motor control apparatus can be achieved that performs angle estimation with a shorter computation time using an inexpensive small-size microprocessor or the like.
The position sensorless motor control apparatus of the invention is characterized in that a voltage, derived by a function that takes a target current of each stator winding of a motor, an actually measured current of the stator winding, and an estimated rotor angle of the motor as variables, is applied to the stator winding of the motor.
The state equation of the control apparatus according to this invention does not contain back electromotive force (electromotive force) or magnetic flux elements. This absence of temperature dependent elements has the effect that the estimation accuracy of the rotor angle of the motor does not degrade due to temperature.
In this specification and in the description of the appended claims, the term xe2x80x9cestimated anglexe2x80x9d refers to the angle that has been estimated, while the term xe2x80x9cestimated angular velocityxe2x80x9d refers to the angular velocity that has been estimated.
In this specification and in the description of the appended claims, the terms xe2x80x9crotor anglexe2x80x9d, xe2x80x9crotor phasexe2x80x9d, and xe2x80x9crotor positionxe2x80x9d are used with the same meaning.
Further, in this specification and in the description of the appended claims, the term xe2x80x9ctarget angular velocityxe2x80x9d is a concept that includes the target number of revolutions that is proportional to the target angular velocity. Likewise, the term xe2x80x9cestimated angular velocityxe2x80x9d is a concept that includes the estimated number of revolutions that is proportional to the estimated angular velocity. The angular velocity and the number of revolutions are substantially the same elements.
The position sensorless motor control apparatus is characterized in that the target current of the stator winding is derived by a function that takes the target angular velocity of the rotor and the estimated angular velocity of the rotor as variables.
The state equation of the control apparatus according to this invention does not contain back electromotive force (electromotive force) or magnetic flux elements. This absence of temperature dependent elements has the effect that the estimation accuracy of the rotor angle of the motor does not degrade due to temperature.
The position sensorless motor control apparatus is characterized by the inclusion of an angle estimating unit for estimating rotor angle of a motor, wherein the angle estimating unit has a first signal or angle information of the first signal, the first signal having the same waveform as the waveform of the phase voltage or phase current or back electromotive force of the stator winding of the motor.
The angle estimating unit in the position sensorless motor control apparatus according this invention has the first signal which, in the case of a three-phase motor driving apparatus, for example, is a signal on the u, v, and w axes. This provides the effect that when performing calculations between the estimated signal and the phase voltage or phase current, etc. of each stator winding of the motor, there is no need for coordinate rotation and the calculations can be performed only on the u, v, and w axes.
If the angle estimating unit has an estimated model (estimated signal) of xcex3xe2x88x92xcex4 axes or the d, q axes, as in the prior art 2, coordinate rotation must be performed when performing calculations between the estimated signal and the phase voltage or phase current, etc. of each stator winding of the motor. If the phase voltage or phase current, etc. of each stator winding of the motor is sinusoidal in waveform, the coordinate rotation is easy, but if the phase voltage, etc. is not sinusoidal in waveform, the coordinate rotation is difficult. In that case, if the same mathematical equations used for the phase voltage, etc. of sinusoidal waveform are used there arises the problem that the estimation error of the rotor angle increases if the coordinates are simply rotated.
For example, when the motor angular velocity or output torque increases and the required phase voltage becomes large, the phase voltage of each stator winding phase saturates, causing the voltage waveform of each phase to lose its sinusoidal shape. In such cases, with an apparatus having an estimated model (estimated signal) of the xcex3xe2x88x92xcex4 axes or the d, q axes, as in the prior art 2, the angle cannot be estimated correctly, and therefore it has not been possible to achieve high angular velocity or large output torque.
By contrast, with the position sensorless motor control apparatus according to the invention, the generation of a non-sinusoidal estimated model (estimated signal) can be easily accomplished because there is no need to rotate the coordinates. This has the effect of being able to achieve high angular velocity and large output torque because the angle can be estimated correctly, even when the motor angular velocity or output torque increases and the required phase voltage becomes large, causing the phase voltage of each stator winding phase to saturate and thereby causing the voltage waveform of each phase to lose its sinusoidal shape.
The equations (2), etc. of the prior art 2 are given on the premise that the permanent magnet of the rotor is magnetized with a sinusoidal waveform, but in the position sensorless motor control apparatus of the invention, the permanent magnet of the rotor can be magnetized with any desired waveform. Accordingly, the invention offers the effect of being able to estimate the rotor angle with high accuracy even for motors whose rotor permanent magnets are magnetized with non-sinusoidal waveforms and whose back electromotive force waveform is non-sinusoidal.
The position sensorless motor control apparatus is characterized in that the stator winding current is treated as a sinusoidal signal.
In the position sensorless motor control apparatus of this invention, since the stator winding current is treated as a sinusoidal signal, it has the effect of simplifying the computation for the angle estimation. This offers the effect that the angle estimation can be accomplished with a short computation time using a small-size and inexpensive microprocessor.
Furthermore, since the stator winding has a large inductance component, the waveform of the stator winding current does not easily""saturate, and even when the waveform of the stator winding phase voltage saturates, the waveform of the phase current is maintained close to a sinusoidal shape; this offers the effect that the angle error arising due to the approximation of the waveform of the stator winding current by a sinusoidal waveform is small even when the waveform of the stator winding phase voltage saturates.
The position sensorless motor control apparatus of the invention is characterized by the inclusion of an angle estimating unit for estimating rotor angle of a motor, wherein the angle estimating unit calculates an angle error between the estimated angle and the angle derived from information containing the phase current of the stator winding of the motor, or calculates an amplitude error having a defined correspondence with the angle error, and corrects the estimated angle in such a manner as to reduce the angle error or the amplitude error having a defined correspondence with the angle error.
While the prior art corrects the waveform of the estimated model in such a manner as to reduce the error between the waveform of the estimated model itself and a signal derived based on measured information, etc., the angle estimating unit in the position sensorless motor control apparatus of this invention calculates a specific parameter of angle error and corrects the estimated angle in such a manner as to reduce the angle error.
For example, when the actual motor driving waveform is a square waveform (or a trapezoidal waveform), the prior art has required that the angle estimating unit have an estimated model of square (or trapezoidal) waveform. By contrast, in the position sensorless motor control apparatus of this invention, the angle estimating unit has an estimated model of sinusoidal waveform; in the above case, the angle estimating unit calculates the angle error between the angle of the square (or trapezoidal) waveform and the angle of the sinusoidal waveform, and corrects the estimated model of sinusoidal waveform in such a manner as to reduce the angle error. This offers the effect of facilitating the generation of the estimated model.
The position sensorless motor control apparatus according to this invention has the effect of being able to achieve high angular velocity and large output torque because the angle can be estimated correctly, even when the motor angular velocity or output torque increases and the required phase voltage becomes large, causing the phase voltage of each stator winding phase to saturate and thereby causing the voltage waveform of each phase to lose its sinusoidal shape.
Furthermore, in the position sensorless motor control apparatus of the invention, the permanent magnet of the rotor can be magnetized with any desired waveform. Accordingly, the invention offers the effect of being able to estimate the rotor angle with high accuracy even for motors whose rotor permanent magnets are magnetized with non-sinusoidal waveforms and whose back electromotive force waveform is non-sinusoidal.
The position sensorless motor control apparatus is characterized by the inclusion of an angle estimating unit for generating an estimated signal containing estimated rotor angle of a motor, wherein the angle estimating unit calculates an angle error between the estimated angle of the estimated signal and the angle derived from information containing the phase current of the stator winding of the motor, or calculates an amplitude error having a defined correspondence with the angle error, and corrects the estimated signal in such a manner as to reduce the angle error or the amplitude error having a defined correspondence with the angle error, and the angle estimating unit further calculates the amplitude error between the amplitude of the estimated signal and the amplitude derived from the information containing the phase current of the stator winding of the motor, and corrects the estimated signal in such a manner as to reduce the amplitude error.
The angle estimating unit in the position sensorless motor control apparatus of this invention calculates specific parameters of angle error and amplitude error and corrects the estimated angle in such a manner as to reduce the angle error. In the position sensorless motor control apparatus of this invention, when the actual motor driving waveform is a square waveform (or a trapezoidal waveform), the angle estimating unit has an estimated model of sinusoidal waveform, calculates the angle error between the angle of the square (or trapezoidal) waveform and the angle of the sinusoidal waveform, and corrects the estimated model of the sinusoidal waveform in such a manner as to reduce the angle error. This offers the effect of facilitating the generation of the estimated model.
If there is an amplitude error between the amplitude of the estimated model and the amplitude of the actual motor signal waveform, there arises the problem that the amplitude error affects the angle error, degrading the angle estimation accuracy. The invention has the effect of being able to calculate the correct angle error with the provision of a feedback loop for reducing the amplitude error. This offers the effect of being able to estimate the angle with high accuracy.
For example, the angle difference (angular velocity time difference) between the estimated model and the signal based on measured results can be directly measured or calculated by providing a counter which takes as a clock input a square wave signal sufficiently faster than the above time, and by starting to count up the counter at a zero crossing point of the estimated model and, at a zero crossing point of the signal based on measure results, latching the count value of the counter into a D flip flops having the same number of stages as the counter. In practice, however, this method of directly measuring or calculating the angle error is difficult to implement, and the accuracy is poor. As a result, in a commonly practiced method the level difference between the two signals is measured or calculated at a particular point in time, and this level difference is converted to the angle error, as in an embodiment of the invention described later. With this method the detection of the error is easier, and the detection accuracy is higher.
The method of converting the level difference to the angle error, however, tends to be affected by signal amplitude errors. The invention is particularly effective for application to apparatuses that detect the angle error using this method.
Further, the level of the signal based on measured results tends to change because of variations in load or in angular velocity. With the provision of the feedback loop for reducing the amplitude error, the invention has the effect of being able to estimate the correct angular velocity even in the presence of variations in load or in angular velocity. This offers the effect of being able to achieve a position sensorless motor control apparatus that estimates the rotor angle with high accuracy over a wide angular velocity range.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit for estimating rotor angle of a motor, the angle estimating unit having a function that takes at least the estimated angle as a variable, wherein the angle estimating unit corrects at least one of coefficients in the function, based on a value derived based on information containing a phase current of a stator winding of the motor.
To drive a position sensorless motor with a sinusoidal waveform requires the provision of an angle estimating unit for estimating the rotor angle of the motor. The angle estimating unit estimates the correct angle by performing control in such a manner as to reduce the angle error between the angle of the estimated model (estimated signal) that the angle estimating unit has and the angle based on the measured result.
When the estimated model has a function that takes the estimated angle as a variable, if a coefficient (for example, signal amplitude) other than the variable (angle) of the function is not correct, the correct angle cannot be estimated.
The angle estimating unit in the position sensorless motor control apparatus of the invention corrects not only the variable but also a coefficient or coefficients in the function, thereby making the function itself match the actual motor; this has the effect of being able to enhance the estimation accuracy of the angle which is the variable.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit for estimating rotor angle of a motor, wherein the transfer characteristics of a signal path leading from an output of the angle estimating unit to a feedback input of the angle estimating unit do not contain back electromotive force, rotor flux linkage, or power generation constants.
As earlier noted the back electromotive force, rotor flux linkage, and power generation constants vary with temperature.
In the position sensorless motor control apparatus of this invention, the transfer characteristics of the signal path leading from the output of the angle estimating unit to the feedback input of the angle estimating unit do not contain the above-listed temperature dependent elements. Accordingly, the invention offers the effect that the angle estimation accuracy of the angle estimating unit does not degrade due to variations in temperature.
In this specification and in the description of the appended claims, the term xe2x80x9cback electromotive forcexe2x80x9d the same in meaning as the term xe2x80x9cpower generation voltagexe2x80x9d. The term xe2x80x9cpower generation constantxe2x80x9d is the same in meaning as the terms xe2x80x9cback electromotive force constantxe2x80x9d and xe2x80x9celectromotive force constantxe2x80x9d.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit for estimating rotor angle of a motor, wherein the angle estimating unit selects a stator winding phase of the motor, and corrects the estimated angle, based on the phase voltage, phase current, or back electromotive force of the selected phase.
The angle estimating unit estimates the correct angle by correcting its internal estimated model, based on a signal or value obtained based on measured results. However, if the correction is made always based on a single signal (for example, the phase voltage of a particular phase (u axis)), there occur angles where the angle error detection accuracy is high and angles where the detection accuracy is low. This leads to the problem that the angle estimation accuracy increases or decreases depending on the angle.
By selecting from among the plurality of stator winding phases the phase for which the largest angle error can be detected and by correcting the estimated angle based on the phase voltage, etc. of the selected phase, the position sensorless motor control apparatus of this invention has the effect of being able to estimate the angle with high accuracy at all times for any rotor angle.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit that has an estimated signal containing information on rotor angle of a motor, wherein when an error between the value derived from information containing a stator winding current of the motor and the value derived from the estimated signal exceeds a predetermined range, it is determined that the motor is not properly controlled.
The position sensorless motor control apparatus estimates the rotor angle of the motor based on measured data, etc., but when the angle estimation error exceeds a certain range for any reason (and as a result, the estimated angular velocity shows a value entirely different from the actual angular velocity), if the estimated angle is thereafter corrected based on measured data, etc., the correction cannot be made correctly, and the correct angle cannot be estimated as long as this condition continues (the angle estimation control does not settle).
The position sensorless motor control apparatus of this invention has the effect of being able to detect the condition when the angle estimation error exceeds a certain range. Accordingly, if a situation arises where the angle estimation control cannot be made to settle forever by an ordinary feedback loop, alternative means, such as stopping the motor, can be taken to quickly exit from the uncontrollable state.
The position sensorless motor control apparatus is also characterized in that when the error exceeds the predetermined range, the motor is decelerated or stopped.
The position sensorless motor control apparatus of this invention has the effect that when the angle estimation error is detected having exceeded the predetermined range, the motor is decelerated or stopped. In particular, when the motor is stopped the angle estimation control can be brought back to the normal condition without fail. It also has the effect that by decelerating the motor, the angle estimation control can be brought back to the normal condition with high probability.
For example, in a position sensorless motor control apparatus having an angle estimating unit for high speed rotation and an angle estimating unit for slow speed rotation, if the angle estimating unit for high speed rotation is thrown into an uncontrollable state during high speed rotation, the motor is decelerated and the angle estimation is performed using the angle estimating unit for slow speed rotation; then, when the correct estimated angle is obtained the motor is accelerated again and the angle estimation is resumed using the angle estimating unit for high speed rotation.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit that has an estimated signal containing information on rotor angle and angular velocity of a motor, wherein the angle estimating unit generates an error signal representative of an error between the value derived from information containing a stator winding current of the motor and the value derived from the estimated signal, and corrects the estimated signal by using a value obtained by multiplying the error signal by a gain having a defined correspondence with the angular velocity.
If the estimated signal is corrected using a correction value obtained by multiplying the error signal by a fixed gain, the problem is that the correction value is too large when the angular velocity of the motor is low, and too small when the angular velocity of the motor is high.
Since the estimated model is corrected using the correction value obtained by multiplying the error signal by a gain having a defined correspondence with the angular velocity, the angle estimating unit in the position sensorless motor control apparatus of this invention has the effect of being able to obtain a proper correction value from a low angular velocity range to a high angular velocity range, achieving high accuracy angle estimation over a wide velocity range.
The position sensorless motor control apparatus is also characterized in that the absolute value of the gain may become larger as the angular velocity increases, but does not become smaller.
The angle estimating unit in the position sensorless motor control apparatus of this invention corrects the estimated model by using a correction value obtained by multiplying the error signal by a small gain when the angular velocity is low, and using a correction value obtained by multiplying the error signal by a large gain when the angular velocity is high. This has the effect of being able to obtain a proper correction value from a low angular velocity range to a high angular velocity range, achieving high accuracy angle estimation over a wide velocity range.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit that has an estimated signal containing information on rotor angle and angular velocity of a motor, wherein the angle estimating unit generates an error signal representative of an error between the value derived from information containing a stator winding current of the motor and the value derived from the estimated signal, corrects the estimated signal by using a correction value derived from the error signal, and performs control so that the correction value does not exceed at least one of an upper bound value and a lower bound value having a defined correspondence with the angular velocity.
The position sensorless motor control apparatus of this invention has the effect of preventing the estimated signal from being corrected using an excessively large correction value. This prevents the problem of the estimated signal varying greatly and drifting outside the pull-in range or hold range of the angle estimating unit, for example, when an erroneous error signal is produced due to transitory noise.
The position sensorless motor control apparatus is also characterized in that the absolute value of the upper bound value or lower bound value may become larger as the angular velocity increases, but does not become smaller.
The position sensorless motor control apparatus of this invention prevents the estimated signal from being corrected using an excessively large correction value; here, the determination level used to determine whether the correction value is excessively large or not varies depending on the angular velocity of the motor. Accordingly, by varying the upper bound value or lower bound value of the correction value in accordance with the angular velocity, an appropriate upper bound value or lower bound value can be set from a low angular velocity range to a high angular velocity range, achieving the effect of being able to perform angle estimation unaffected by noise over a wide velocity range.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit further has a table of compensation values with at least one of the estimated angle, the estimated angular velocity of the motor, and the measured or calculated current of the stator winding taken as a parameter, and in that the angle estimating unit compensates the estimated angle by using the compensation value associated with the parameter.
By including the table of compensation values associated with the parameter, the angle estimating unit of this invention has the effect of being able to estimate the angle with a higher accuracy than an apparatus that estimates the angle by calculation only.
The position sensorless motor control apparatus is also characterized by the inclusion of: a current sensor for detecting a phase current value representing the value of a current to the stator winding of the motor; a voltage command value generating unit for generating, based on estimated rotor angle of the motor, a phase voltage command value indicating a command value for the voltage to be applied to the stator winding; a driving unit for applying the voltage to the stator winding based on the phase voltage command value; an angle estimating unit for generating the estimated angle; and a rotational direction command unit for outputting a rotational direction command indicating the direction in which the rotor is to be rotated, wherein when the rotational direction commands indicates a reverse direction, the phase current values for at least two phases are interchanged with each other and the phase voltage command values for the at least two phases are interchanged with each other.
This invention has the effect of being able to realize a position sensorless motor control apparatus that accomplishes switching between the forward and reverse rotations with a very small number of elements involved, and that allows most of the circuit block or program block to be used for both forward and reverse rotations.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit for estimating rotor angle of a motor, wherein the angle estimating unit has a second signal or a third signal derivable from the second signal, or angle information of the second signal or third signal, the second signal having the same waveform as the waveform of a back electromotive force derived by subtracting components other than the back electromotive force from the measured or calculated phase voltage of the stator winding.
This invention derives the back electromotive force by subtracting the components other than the back electromotive force from the measured or calculated voltage of the stator winding.
If the estimated signal is generated using the back electromotive force, as in the prior art, the angle estimation accuracy degrades since the back electromotive force changes with temperature. For example, with the method of obtaining the back electromotive force from the equations (87) and (88), as in the prior art 2, the derived estimated angle Em has temperature dependence.
By contrast, the position sensorless motor control apparatus of the invention derives the back electromotive force by subtracting the components other than the back electromotive force from the measured or calculated voltage of the stator winding, and thus can obtain the correct back electromotive force. Though the magnitude of this back electromotive force has temperature dependence, this will have no ill effect on the angle estimation since the magnitude relationships between the back electromotive force on the u axis, the back electromotive force on the v axis, and the back electromotive force on the w axis are not temperature dependent. The invention therefore has the effect of being able to realize an angle estimating unit having a high estimation accuracy over a wide temperature range.
Basically, the angle estimating unit of this invention takes as the estimated. signal the second signal having the same waveform as the waveform of the back electromotive force of one of the u, v, and w phases (in the case of a three-phase motor). However, this is not restrictive; for example, the angle estimating unit may be configured to have a third signal derivable from the second signal, for example, a back electromotive force expressed on the xcex3xe2x88x92xcex4 (or d, q) axes. The two signals are compatible with each other and have the same effect in addressing the above problem.
Further, the angle estimating unit may be configured to have the waveform of the second signal, which is, for example, a sinusoidal wave, in its original form, or have only the angle information in the form of numeric information.
This includes, for example, the case in which the phase voltage applied to the stator winding of the motor is of a square or trapezoidal waveform and the estimated model is a sinusoidal wave having the same angle as that of the waveform of the phase voltage applied to the stator winding. This sinusoidal wave contains the angle information of the phase voltage of square or trapezoidal waveform.
Preferably, the angle estimating unit has the back electromotive force of one of the u, v, and w phases (in the case of a three-phase motor) as the estimated signal, as described above, because it then facilitates the generation of the estimated model of a non-sinusoidal waveform.
The position sensorless motor control apparatus is also characterized in that the second signal or third signal or the angle information is derived by a function that takes the measured or calculated phase voltage of the stator winding of the motor, the measured current of the stator winding, and the estimated rotor angle of the motor as variables.
This invention derives the back electromotive force based on the measured or phase voltage of the stator winding, the measured phase current of the stator winding, etc. that do not have temperature dependence, or on the measured phase voltage of the stator winding, etc. The angle estimated using the back electromotive force derived based on these elements is unaffected by temperature variations, as previously described the invention has the effect of providing an angle estimating unit capable of estimating the angle with high accuracy over a wide temperature range.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit calculates an angle error between a signal derived from the second signal or the third signal, or a signal derived from the angle information, and the back electromotive force derived by subtracting the components other than the back electromotive force from the measured or calculated phase voltage of the stator winding, or calculates an amplitude error having a defined correspondence with the angle error, and corrects the estimated angle of the second signal or third signal or of the angle information in such a manner as to reduce the angle error or the amplitude error having a defined correspondence with the angle error.
In the position sensorless motor control apparatus of this invention, even when the back electromotive force waveform of the actual motor is a square waveform (or a trapezoidal waveform), the angle estimating unit has an estimated model of sinusoidal waveform, calculates the angle error between the angle of the square (or trapezoidal) waveform and the angle of the sinusoidal waveform, and corrects the estimated model of the sinusoidal waveform in such a manner as to reduce the angle error. This offers the effect of facilitating the generation of the estimated model by eliminating the need to generate an estimated model of the square (or trapezoidal) waveform.
Accordingly, the position sensorless motor control apparatus of this invention has the effect of being able to achieve high angular velocity and large output torque because the angle can be estimated correctly, even when the motor angular velocity or output torque increases and the required phase voltage becomes large, causing the phase voltage of each stator winding phase to saturate and thereby causing the voltage waveform of each phase to lose its sinusoidal shape.
Furthermore, in the position sensorless motor control apparatus of the invention, the permanent magnet of the rotor can be magnetized with any desired waveform. Accordingly, the invention offers the effect of being able to estimate the rotor angle with high accuracy even for motors whose rotor permanent magnets are magnetized with non-sinusoidal waveforms and whose back electromotive force waveform is non-sinusoidal.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit further calculates an amplitude error between the amplitude of the second signal or third signal and the amplitude of the back electromotive force derived by subtracting the components other than the back electromotive force from the measured or calculated phase voltage of the stator winding, and corrects the amplitude of the second signal or third signal in such a manner as to reduce the amplitude error.
The position sensorless motor control apparatus of this invention has the effect of being able to calculate the correct angle error with the provision of the feedback loop for reducing the amplitude error between the amplitude of the estimated model and the amplitude of the actual motor signal waveform when the amplitude error adversely affects the angle estimation. This offers the effect of being able to estimate the angle with high accuracy.
This invention is particularly effective for application to an apparatus that detects angle error by measuring or calculating the level difference between the two signals at a particular point in time and by converting the level difference to the angle error.
There is also offered the effect of being able to estimate the correct angular velocity even when the signal amplitude changes because of changes in load or in angular velocity. The resulting effect is the realization of a position sensorless motor control apparatus that estimates the rotor angle with high accuracy over a wide angular velocity range.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit that has a back electromotive force estimated signal containing information on rotor angle of a motor, wherein the angle estimating unit selects the largest error from among errors each representing an error between the back electromotive force of each phase, derived based on information containing the current of each stator winding phase of the motor, and the estimated signal of the back electromotive force, and corrects the estimated signal in such a manner as to reduce the largest error.
The angle estimating unit estimates the correct angle by correcting its internal estimated model, based on a signal or value obtained based on measured results. However, if the correction is made always based on the back electromotive force of a particular phase (u axis), there occur angles where the angle error detection accuracy is high and angles where the detection accuracy is low. This leads to the problem that the angle estimation accuracy increases or decreases depending on the angle.
By selecting from among the plurality of stator winding phases the phase for which the largest angle error can be detected and by correcting the estimated angle based on the back electromotive force of the selected phase, the position sensorless motor control apparatus of this invention has the effect of being able to estimate the angle with high accuracy at all times for any rotor angle.
The calculation of the xe2x80x9cerror between the back electromotive force of each phase and the estimated signal of the back electromotive forcexe2x80x9d means calculating the error by considering the angular displacement of each phase (in the case of a three-phase motor, the phases are displaced relative to each other by 120 degrees).
Suppose, for example, that the estimated signals of the back electromotive forces for the respective phases have a prescribed angle on the u, v, and w axes.
In one embodiment, the back electromotive force of each phase is coordinate converted so that its angle matches the angle of the estimated signal, and the error between the estimated signal and the back electromotive force after the coordinate conversion is calculated.
In another embodiment, the estimated signal is coordinate converted so that its angle matches the angle of each phase, and the error between the back electromotive force of each phase and the estimated signal after the coordinate conversion is calculated.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit that has a back electromotive force estimated signal containing information on rotor angle of a motor, wherein the angle estimating unit selects a stator winding phase whose back electromotive force is the smallest of the back electromotive forces of the stator winding phases of the motor derived based on information respectively containing the currents of the respective stator winding phases, and corrects the estimated signal in such a manner as to reduced an error between the back electromotive force of the selected phase and the estimated signal of the back electromotive force.
By selecting from among the plurality of stator winding phases the phase for which the largest angle error can be detected and by correcting the estimated angle based on the back electromotive force of the selected phase, the position sensorless motor control apparatus of this invention has the effect of being able to estimate the angle with high accuracy at all times for any rotor angle.
Further, a simple method is used that compares the back electromotive forces of the respective phases and selects the phase whose back electromotive force is the smallest, eliminating the need to calculate errors for all phases; this offers the effect of reducing the computation time, since the phase whose error is the largest in the normal state is selected and the error is calculated only for the selected phase.
The position sensorless motor control apparatus is also characterized in that when the amplitude of the second signal or third signal exceeds a predetermined range, the motor is decelerated or stopped.
The position sensorless motor control apparatus of this invention has the effect of being able to detect the condition when the amplitude of the estimated signal, i.e., the second signal or the third signal, exceeds a certain range. Accordingly, if a situation arises where the angle estimation control cannot be made to settle forever by an ordinary feedback loop, alternative means, such as stopping the motor, can be taken to exit from the uncontrollable state.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit corrects the estimated angle of the second signal or third signal or of the angle information by using a correction value obtained by multiplying the angle error, or the amplitude error having a defined correspondence with the angle error, by a gain having a defined correspondence with the estimated rotor angular velocity of the motor.
Since the estimated model is corrected using a value obtained by multiplying the error signal by a gain having a defined correspondence with the angular velocity, the angle estimating unit in the position sensorless motor control apparatus of this invention has the effect of being able to obtain a proper correction value from a low angular velocity range to a high angular velocity range, achieving high accuracy angle estimation over a wide velocity range.
The position sensorless motor control apparatus is also characterized in that the absolute value of the gain may become larger as the angular velocity increases, but does not become smaller.
The angle estimating unit in the position sensorless motor control apparatus of this invention corrects the estimated model by using a correction value obtained by multiplying the error signal by a small gain when the angular velocity is low, and using a correction value obtained by multiplying the error signal by a large gain when the angular velocity is high. This has the effect of being able to obtain a proper correction value from a low angular velocity range to a high angular velocity range, achieving high accuracy angle estimation over a wide velocity range.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit performs control so that the correction value does not exceed at least one of the upper bound value and lower bound value having a defined correspondence with the angular velocity.
The position sensorless motor control apparatus of this invention has the effect of preventing the estimated signal from being corrected using an excessively large correction value. This prevents the problem of the estimated signal varying greatly and drifting outside the pull-in range or hold range of the angle estimating unit, for example, when an erroneous error signal is produced due to transitory noise.
The position sensorless motor control apparatus is also characterized in that the absolute value of the upper bound value or lower bound value may become larger as the angular velocity increases, but does not become smaller.
The position sensorless motor control apparatus of this invention prevents the estimated signal from being corrected using an excessively large correction value; here, the determination level used to determine whether the correction value is excessively large or not varies depending on the angular velocity of the motor. Accordingly, by varying the upper bound value or lower bound value of the correction value in accordance with the angular velocity, an appropriate upper bound value or lower bound value can be set from a low angular velocity range to a high angular velocity range, achieving the effect of being able to perform angle estimation unaffected by noise over a wide velocity range.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit further has a table of compensation values with at least one of the estimated angle, the estimated angular velocity of the motor, and the measured or calculated current of the stator winding taken as a parameter, and corrects and compensates the estimated angle of the second signal or third signal or of the angle information by using the compensation value associated with the parameter in the table as well as the compensation value derived from the angle error or the amplitude error having a defined correspondence with the angle error.
By including the table of compensation values associated with the parameter, the angle estimating unit of this invention has the effect of being able to estimate the angle with a higher accuracy than an apparatus that estimates the angle by calculation only.
The position sensorless motor control apparatus is also characterized in that the components other than the back electromotive force are derived using the measured or calculated current of the stator winding of the motor, the measured or calculated current being assumed to be a sinusoidal signal.
In the position sensorless motor control apparatus of this invention, since the stator winding current is treated as a sinusoidal signal, it has the effect of simplifying the computation for the angle estimation. This offers the effect that the angle estimation can be accomplished with a short computation time using a small-size and inexpensive microprocessor.
Furthermore, since the stator winding has a large inductance component, the waveform of the stator winding current does not easily saturate, and even when the waveform of the stator winding phase voltage saturates, the waveform of the phase current is maintained close to a sinusoidal shape; this offers the effect that the angle error arising due to the approximation of the waveform of the stator winding current by a sinusoidal waveform is small even when the waveform of the stator winding phase voltage saturates.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit for estimating rotor angle of a motor, wherein the angle estimating unit has a fourth signal or a fifth signal derivable from the fourth signal, or angle information of the fourth signal or fifth signal, the fourth signal having the same waveform as the waveform of a stator winding current.
The position sensorless motor control apparatus of this invention estimates the angle by reference to the current signal of the stator winding. As shown in equation (72), the angle error of the estimated angle derived from the back electromotive force is equivalent to the angle error of the estimated angle derived from the stator winding current. Accordingly, the estimated angle derived from the current is stable to temperature. Generally, the current value of the stator winding is stable to temperature.
The invention therefore has the effect of being able to realize an angle estimating unit having a high estimation accuracy over a wide temperature range.
Basically, the angle estimating unit of this invention takes as the estimated signal the fourth signal having the same waveform as the waveform of the phase current of one of the u, v, and w phases (in the case of a three-phase motor). However, this is not restrictive; for example, the angle estimating unit may be configured to have a fifth signal derivable from the fourth signal, for example, a stator winding current signal expressed on the xcex3xe2x88x92xcex4 (or d, q) axes. The two signals are compatible with each other and have the same effect in addressing the above problem.
Further, the angle estimating unit may be configured to have the waveform of the fourth signal or fifth signal, which is, for example, a sinusoidal wave, in its original form, or have only the angle information in the form of numeric information.
This includes, for example, the case in which the phase current applied to the stator winding of the motor is of a square waveform and the estimated model is a sinusoidal wave having the same angle as that of the waveform of the phase current applied to the stator winding. This sinusoidal wave contains the angle information of the phase current of square waveform.
Preferably, the angle estimating unit has the phase current of one of the u, v, and w phases (in the case of a three-phase motor) as the estimated signal, as described above, because it then facilitates the generation of the estimated model of a non-sinusoidal waveform (since coordinate rotation is not needed).
The position sensorless motor control apparatus is also characterized in that the angle estimating unit calculates an angle error between the fourth signal or fifth signal or the angle information and the signal derived from the stator winding current, or calculates an amplitude error having a defined correspondence with the angle error, and corrects the estimated angle of the fourth signal or fifth signal or of the angle information in such a manner as to reduce the angle error or the amplitude error having a defined correspondence with the angle error.
In the position sensorless motor control apparatus of this invention, even when the current waveform of the actual motor is a square waveform, the angle estimating unit has an estimated model of sinusoidal waveform, calculates the angle error between the angle of the square waveform and the angle of the sinusoidal waveform, and corrects the estimated model of the sinusoidal waveform in such a manner as to reduce the angle error. This offers the effect of facilitating the generation of the estimated model by eliminating the need to generate an estimated model of the square waveform.
Accordingly, the position sensorless motor control apparatus of this invention has the effect of being able to achieve high angular velocity and large output torque because the angle can be estimated correctly, even when the motor angular velocity or output torque increases and the required phase voltage becomes large, causing the phase voltage of each stator winding phase to saturate and thereby causing the voltage waveform of each phase to lose its sinusoidal shape.
Furthermore, in the position sensorless motor control apparatus of the invention, the permanent magnet of the rotor can be magnetized with any desired waveform. Accordingly, the invention offers the effect of being able to estimate the rotor angle with high accuracy even for motors whose rotor permanent magnets are magnetized with non-sinusoidal waveforms and whose back electromotive force waveform is non-sinusoidal.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit further calculates an amplitude error between the amplitude of the fourth signal or fifth signal that the angle estimating unit has and the amplitude of the signal derived from the stator winding current, and corrects the amplitude of the fourth signal or fifth signal in such a manner as to reduce the amplitude error.
The position sensorless motor control apparatus of this invention has the effect of being able to calculate the correct angle error with the provision of the feedback loop for reducing the amplitude error between the amplitude of the estimated model and the amplitude of the actual motor signal waveform when the amplitude error adversely affects the angle estimation. This offers the effect of being able to estimate the angle with high accuracy.
This invention is particularly effective for application to an apparatus that detects angle error by measuring or calculating the level difference between the two signals at a particular point in time and by converting the level difference to the angle error.
There is also offered the effect of being able to estimate the correct angular velocity even when the signal amplitude changes because of changes in load or in angular velocity. The resulting effect is the realization of a position sensorless motor control apparatus that estimates the rotor angle with high accuracy over a wide angular velocity range.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit that has a stator winding current estimated signal containing information on rotor angle of a motor, wherein the angle estimating unit selects the largest error from among errors each representing an error between a measured current of each stator winding of the motor and the estimated signal of the current, and corrects the estimated signal in such a manner as to reduce the largest error.
The angle estimating unit estimates the correct angle by correcting its internal estimated model, based on a signal or value obtained based on measured results. However, if the correction is made always based on the phase current of a particular phase (u axis), there occur angles where the angle error detection accuracy is high and angles where the detection accuracy is low. This leads to the problem that the angle estimation accuracy increases or decreases depending on the angle.
By selecting from among the plurality of stator winding phases the phase for which the largest angle error can be detected and by correcting the estimated angle based on the phase current of the selected phase, the position sensorless motor control apparatus of this invention has the effect of being able to estimate the angle with high accuracy at all times for any rotor angle.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit that has a stator winding current estimated signal containing information on rotor angle of a motor, wherein the angle estimating unit selects a stator winding phase whose measured current is the smallest of the measured currents of the stator winding phases of the motor, and corrects the estimated signal in such a manner as to reduced the error between the current of the selected phase and the estimated signal of the current.
By selecting from among the plurality of stator winding phases the phase for which the largest angle error can be detected and by correcting the estimated angle based on the phase current of the selected phase, the position sensorless motor control apparatus of this invention has the effect of being able to estimate the angle with high accuracy at all times for any rotor angle.
Further, a simple method is used that compares the back electromotive forces of the respective phases and selects the phase whose back electromotive force is the smallest, eliminating the need to calculate errors for all phases; this offers the effect of reducing the computation time, since the phase whose error is the largest in the normal state is selected and the error is calculated only for the selected phase.
The position sensorless motor control apparatus is also characterized in that when the angle error or the amplitude error having a defined correspondence with the angle error exceeds a predetermined range, the motor is decelerated or stopped.
The position sensorless motor control apparatus of this invention has the effect of being able to detect the condition when the angle estimation error exceeds a certain range. Accordingly, if a situation arises where the angle estimation control cannot be made to settle forever by an ordinary feedback loop, alternative means, such as stopping the motor, can be taken to exit from the uncontrollable state.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit corrects the estimated angle of the fourth signal or fifth signal or of the angle information by using a correction value obtained by multiplying the angle error, or the amplitude error having a defined correspondence with the angle error, by a gain having a defined correspondence with the estimated rotor angular velocity of the motor.
Since the estimated model is corrected using a value obtained by multiplying the error signal by a gain having a defined correspondence with the angular velocity, the angle estimating unit in the position sensorless motor control apparatus of this invention has the effect of being able to obtain a proper correction value from a low angular velocity range to a high angular velocity range, achieving high accuracy angle estimation over a wide velocity range.
The position sensorless motor control apparatus is also characterized in that the absolute value of the gain may become larger as the angular velocity increases, but does not become smaller.
The angle estimating unit in the position sensorless motor control apparatus of this invention corrects the estimated model by using a correction value obtained by multiplying the error signal by a small gain when the angular velocity is low, and using a correction value obtained by multiplying the error signal by a large gain when the angular velocity is high. This has the effect of being able to obtain a proper correction value from a low angular velocity range to a high angular velocity range, achieving high accuracy angle estimation over a wide velocity range.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit performs control so that the correction value does not exceed at least one of the upper bound value and lower bound value having a defined correspondence with the angular velocity.
The position sensorless motor control apparatus of this invention has the effect of preventing the estimated signal from being corrected using an excessively large correction value. This prevents the problem of the estimated signal varying greatly and drifting outside the pull-in range or hold range of the angle estimating unit, for example, when an erroneous error signal is produced due to transitory noise.
The position sensorless motor control apparatus is also characterized in that the absolute value of the upper bound value or lower bound value may become larger as the angular velocity increases, but does not become smaller.
The position sensorless motor control apparatus of this invention prevents the estimated signal from being corrected using an excessively large correction value; here, the determination level used to determine whether the correction value is excessively large or not varies depending on the angular velocity of the motor. Accordingly, by varying the upper bound value or lower bound value of the correction value in accordance with the angular velocity, an appropriate upper bound value or lower bound value can be set from a low angular velocity range to a high angular velocity range, achieving the effect of being able to perform angle estimation unaffected by noise over a wide velocity range.
The position sensorless motor control apparatus is also characterized in that the angle estimating unit has a table of compensation values with at least one of the estimated angle, the estimated angular velocity of the rotor, and the measured or calculated current of the stator winding taken as a parameter, and compensates the estimated angle of the fourth signal or fifth signal or of the angle information by using the compensation value associated with the parameter in the table.
By including the table of compensation values associated with the parameter, the angle estimating unit of this invention has the effect of being able to estimate the angle with a higher accuracy than an apparatus that estimates the angle by calculation only.
The position sensorless motor control apparatus is also characterized in that the measured or calculated current of the stator winding of the motor is treated as a sinusoidal signal.
In the position sensorless motor control apparatus of this invention, since the stator winding current is treated as a sinusoidal signal, it has the effect of simplifying the computation for the angle estimation. This offers the effect that the angle estimation can be accomplished with a short computation time using a small-size and inexpensive microprocessor.
Furthermore, since the stator winding has a large inductance component, the waveform of the stator winding current does not easily saturate, and even when the waveform of the stator winding phase voltage saturates, the waveform of the phase current is maintained close to a sinusoidal shape; this offers the effect that the angle error arising due to the approximation of the waveform of the stator winding current by a sinusoidal waveform is small even when the waveform of the stator winding phase voltage saturates.
The position sensorless motor control apparatus is also characterized by the inclusion of an angle estimating unit for estimating rotor angle of a motor, wherein the angle estimating unit has a sixth signal or a seventh signal derivable from the sixth signal, or angle information of the sixth signal or seventh signal, the sixth signal having the same waveform as the waveform of the measured or calculated phase voltage of the stator winding.
By taking as the estimated model a signal having the same waveform as the waveform of the measured or calculated phase voltage of the stator winding, the position sensorless motor control apparatus of this invention has the effect of being able to perform angle estimation using an inexpensive small-size microprocessor or the like and reducing the computation time.